Answer
The roots of these closely spaced white spruce became naturally grafted together over time, forming, in essence, a single organism. So when some of the trees were cut down, the communal root system responded as it would to an injury and attempted to callus over the stumps. These two pieces: Why should trees have natural root grafts? and Is root grafting a positive, cooperative behavior in trees? shed a little more light on the phenomenon of natural root grafting.
This week’s contest winner was John Patterson